问题
I have two tables orders
and orderdetails
table orders (PK = id, UNIQUE index on orderno)
|id|orderno|
| 1|1000 |
| 2|1001 |
table orderdetails (PK = id)
|id|orderid|item|qty|
| 1| 1|ABC | 3|
| 2| 1|XYZ | 4|
Now I want to query the data with:
SELECT o.orderno, od.item, od.qty
FROM orders o
INNER JOIN orderdetails od ON o.orderno = od.order
which returns:
|orderno|item|qty|
|1000 |ABC | 3|
|1000 |XYZ | 4|
However If I use the following code to load the result into a DataTable it fails:
var connectionString = "Server=localhost;Database=orders;Uid=root;";
var commandText = "SELECT o.orderno, od.item, od.qty" + Environment.NewLine +
"FROM orders o" + Environment.NewLine +
"INNER JOIN orderdetails od ON o.orderno = od.order";
var reader = MySqlHelper.ExecuteReader(connectionString, commandText);
var table = new DataTable("OrdersQuery");
table.Fill(reader); // throws ConstraintException
The problem is, that
table.Constraints[0]
is a UniqueConstraints
on the orderno column. Propably because
reader.GetSchemaTable()
has a IsUnique=true
entry for orderno (which is true in the base table, but not true for the join query).
Even worse, that doesn't help either:
table.BeginLoadData(); // msdn docs claim that this should disable constraints
table.Load(reader);
table.EndLoadData();
Any ideas how to fix this?
StackTrace:
System.Data.ConstraintException Was Unhandled.
Message=Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.
Source=System.Data
StackTrace:
bei System.Data.DataTable.EnableConstraints()
bei System.Data.DataTable.set_EnforceConstraints(Boolean value)
bei System.Data.DataTable.EndLoadData()
bei System.Data.Common.DataAdapter.FillFromReader(DataSet dataset, DataTable datatable, String srcTable, DataReaderContainer dataReader, Int32 startRecord, Int32 maxRecords, DataColumn parentChapterColumn, Object parentChapterValue)
bei System.Data.Common.DataAdapter.Fill(DataTable[] dataTables, IDataReader dataReader, Int32 startRecord, Int32 maxRecords)
bei System.Data.Common.LoadAdapter.FillFromReader(DataTable[] dataTables, IDataReader dataReader, Int32 startRecord, Int32 maxRecords)
bei System.Data.DataTable.Load(IDataReader reader, LoadOption loadOption, FillErrorEventHandler errorHandler)
bei System.Data.DataTable.Load(IDataReader reader)
回答1:
I had the same problem but got it fixed by using the workaround from this post: http://bugs.mysql.com/bug.php?id=65065 (at bottom):
cmd.CommandText = "SELECT cam.no_serie, t.mnt FROM trx t LEFT JOIN camn cam USING(id_camn) ";
MySqlDataReader dr = cmd.ExecuteReader();
DataSet ds = new DataSet();
DataTable dataTable = new DataTable();
ds.Tables.Add(dataTable);
ds.EnforceConstraints = false;
dataTable.Load(dr);
dr.Close();
回答2:
I just figured out, that
table.Fill(reader)
does not create the constraint, if I already added the columns.
So I fixed this by using a nice little extension method:
public static void Load(this DataTable table, IDataReader reader, bool createColumns)
{
if (createColumns)
{
table.Columns.Clear();
var schemaTable = reader.GetSchemaTable();
foreach (DataRowView row in schemaTable.DefaultView)
{
var columnName = (string)row["ColumnName"];
var type = (Type)row["DataType"];
table.Columns.Add(columnName, type);
}
}
table.Load(reader);
}
Usage:
table.Fill(reader, true);
回答3:
There is simple dirty way how to fix it - surround column in query with unique contraint with concat function:
var commandText = "SELECT CONCAT(o.orderno, ''), od.item, od.qty ...";
回答4:
I had the same error today and want to share.My problem was a column with a LONGTEXT type. If I include LONGTEXT column in my query and tried to load dataset without specifying column names exception was thrown. Based on SchlaWiener's code I rewrote the code as follows and everything is fine now.
MySqlDataReader resultSet = cmd.ExecuteReader();
dt.Columns.Clear();
for (int i = 0; i < resultSet.FieldCount; i++)
{
dt.Columns.Add(resultSet.GetName(i));
}
dt.Load(resultSet);
回答5:
MySQL allows multiple null values in unique indexes. This causes ConstraintException on fill. How to fix: find this constraint in the 'table.Constraints' list and remove it or just clear all constraints.
回答6:
I had a similar problem with the queries, when loading the Datatable () with the MYSQL Reader it generated error NON-NULL, UNIQUE or FOREIGN-KEY.
In the end I solved it by changing the MySQL Connector.NET version.
https://dev.mysql.com/downloads/connector/net/
来源:https://stackoverflow.com/questions/7580929/mysqldatareader-datatable-fillreader-throws-constraintexception